Twin-chamber Knudsen effusion cell source mass spectrometry: vaporization of palladium

Abstract A novel vapor source for high temperature mass spectrometry has been developed recently in our laboratory. With this twin-chamber Knudsen cell source the vaporization of a sample can be compared simultaneously with a vapor pressure reference material ( e.g. gold). This eliminates many errors due to the usual calibration with silver or gold. The vapor pressure of pure palladium is redetermined using this vapor source with gold as the reference substance from 1450 K to the melting point of palladium. The enthalpy of sublimation, ΔH v o ( Pd , 298 K ) = 90.3 ± 0.20 kcal mol −1 , obtained from the third law treatment of the data is in excellent agreement with the corresponding enthalpy value of 90.0 ± 0.5 kcal mol −1 recommended by Hultgren et al. , and also with the value of 89.8 ± 0.8 kcal mol −1 deduced from the second law method. The temperature dependence of the vapor pressure of palladium is calculated to be lg( p atm ) = (6.12 ± 0.02) − (19230 ± 200) T This value of equilibrium pressure is probably the best value for this parameter.